A thermistor is a resistive device whose resistance varies with temperature changes. Thermistors are used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulating elements. One specific application of thermistors is in instruments used for oil field exploration.
Because of their resistance-temperature dependence, thermistors are used as temperature sensors, and as such, thermistors typically achieve high precision relative to other temperature sensing elements, but do so within a limited temperature range, usually −90° C. to +130° C. However, platinum (Pt) thermistors are commercially available, and can be used at elevated temperatures, in the range of 500° C. to 700° C. More recently, semiconductors, including diamond-based semiconductors, have been considered for use in high temperature thermistors because of their thermal stability and an exponential temperature of the resistance, namely R(T)˜exp(Ea/kBT), where Ea is the activation energy. However, at temperatures above 800° C., the diamond surface transforms to a graphite layer, thus limiting diamond-based semiconductor thermistor's temperature operational range to less than 800° C.